I've actually gotten a pair of rabbits from them (Bunny World Foundation) but that was almost 20 years ago now. I think then it was $250 for a bonded pair (fixed).
Adoption costs vary wildly per location. It will be cheaper in the midwest and always most expensive in CA. Have you called around to find out what it costs to neuter or spay a rabbit? I'm in AZ. My cost to spay a single female is $250. So buying an already fixed pair for $250 is still a bargain. In that light, $195 for a single spayed rabbit is still a bargain. Our local rescue in AZ charges $75 for a single rabbit and $140 for a pair. I went with BWF that one time because I fell in love with the blue-eyed bonded pair.
Have you let BWF know that you already have a bonded pair?? Are they willing to take the rabbit back if it doesn't bond with your pair? It can be extremely difficult to introduce a 3rd rabbit to an existing pair. It risks the bond of the original pair. You could end up with the new one bonding with just one of your rabbits and the remaining one being left without a bondmate. What would BWF do in that instance? I'd more concerned about their return policy and how they handle that, then I would be about their price.